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Mastering Functional Programming
Mastering Functional Programming

Mastering Functional Programming: Functional techniques for sequential and parallel programming with Scala

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Mastering Functional Programming

Functions and Lambdas

The paradigm of functional programming has a lot of common features with the paradigm of declarative programming. One of the defining features of functional languages and declarative programming is the extensive use of functions. This chapter will discuss in more detail what functions are and their meaning in different paradigms. We will have a look at how we can use functions and what their role is in modern programming languages.

In this chapter, we will cover the following topics:

  • Functions as behaviors
  • Functions in functional programming
  • Higher-order functions
  • Lambdas
  • The concept of functions in different programming languages

Functions as behavior

So what are functions? We can define them as parameterized, named chunks of code. This means that they are chunks of code that can be called from any other part of the program by their name. Parameterized means that you can call them with certain arguments. Different calls executed with different parameters usually lead to different results.

What is the motivation behind functions? The answer is the basic principle of engineering – abstract away that which repeats itself. In Chapter 1, The Declarative Programming Style, we saw something similar in the case of loops. However, loops are built-in control structures. This means they are defined at the language level. When we need to define some logic on the language-user level, and this logic repeats itself across different parts of the project, functions come into play.

We can trace functions across...

Functions in functional programming

In imperative programming, functions are used to represent the behavior of an object. In object-oriented programming, the behavior usually implies side effects. For the purposes of this book, we can understand side effects as follows—a function is side-effecting when it modifies the environment outside its own body. For example, it can have a global variable of its parent object modified, it can write a file into the filesystem, or the function can perform some web API calls over the network.

In functional programming, the understanding of functions is quite different. In functional programming, we prise purity and referential transparency. Purity means the absence of side effects. Referential transparency means that the result value the function has computed can be substituted in place of the function call, while the semantics of the...

Higher-order functions

Another important concept that appears in functional programming is that of higher-order functions. A higher-order function is a function that accepts a function as an argument. A very trivial example of where this may be useful is control structures. For example, a while loop can be expressed in a functional way as a higher-order function that accepts the body of the loop and a predicate as an argument.

The body of the loop can be expressed as a function that does not accept any arguments, but computes some side effects. The way it works is that we have a function accept a 0-argument function and a predicate, and we call the same loop function recursively while the predicate is true.

We can call the new control structure whileDiy, and it can be defined as follows:

@annotation.tailrec
def whileDiy(predicate: => Boolean)(body: => Unit): Unit =
if ...

Understanding lambda functions

Most functional languages have a concept of a lambda function. It is an anonymous function defined inline. It can be assigned to a variable if needed. For example, consider that we need a function that accepts a cookie with user session data, in the context of a web application. Its job is to print a greeting to the user to the standard output. However, before printing, we need to decorate the user's name in a certain way. To complicate matters further, we also have a database of users who hold PhDs and, if they do, we need to refer to them as Dr. Here is how it can be done in Scala:

  1. We define the dummy Cookie class for our example:
case class Cookie(name: String, gender: String)
  1. We define the greeting method. The job of the method is to extract the data from the cookie object, and apply the modifier to the user's name based on their...

The concept of functions in different programming languages

Functions are present in many programming languages. Some of the languages have better support for purely functional styles, while others favor declarative styles. This is why, for example, using Scala over Java can give you tremendous leverage, because you can declare functions inside other functions, you can declare functions that accept other functions (higher-order functions) more easily, and you can declare anonymous lambda functions (functionality also available in Java, starting from Java 8). This greatly increases your capacity for abstraction, creating control structures, and thereby enabling your application to be expressed in a more DRY (Don't Repeat Yourself) way.

Summary

In this chapter, we have seen what functions are and how they have evolved from the early days of programming to today. We have seen how functions were initially treated as abstractions of common logic. After that, in object-oriented programming, they represented the behavior of certain objects. Object-oriented programmers attempted to represent everything as an object. So it is only natural that functions started to be viewed in the context of a world that consists of objects. In this context, functions are best viewed as behaviors of these objects.

In functional programming, functions can be viewed in a different context. Now, the best way to view functions is as mathematical computations. They compute some value out of its inputs, in a pure way, which means without any side effects. The idea is to view them as mathematical functions.

Functional programming is close...

Questions

  1. How are functions interpreted in the context of object-oriented programming?
  2. How are functions interpreted in the context of pure functional programming?
  3. What are higher-order functions?
  4. Why are higher-order functions useful?
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Key benefits

  • Learn functional programming from scratch
  • Program applications with pure functions to rule out side effects
  • Gain expertise in working with array tools for functional programming

Description

Functional programming is a paradigm specifically designed to deal with the complexity of software development in large projects. It helps developers to keep track of the interdependencies in the code base and changes in its state in runtime. Mastering Functional Programming provides detailed coverage of how to apply the right abstractions to reduce code complexity, so that it is easy to read and understand. Complete with explanations of essential concepts, practical examples, and self-assessment questions, the book begins by covering the basics such as what lambdas are and how to write declarative code with the help of functions. It then moves on to concepts such as pure functions and type classes, the problems they aim to solve, and how to use them in real-world scenarios. You’ll also explore some of the more advanced patterns in the world of functional programming such as monad transformers and Tagless Final. In the concluding chapters, you’ll be introduced to the actor model, which you can implement in modern functional languages, and delve into parallel programming. By the end of the book, you will be able to apply the concepts of functional programming and object-oriented programming (OOP)in order to build robust applications.

Who is this book for?

If you are from an imperative or OOP background, this book will guide you through the world of functional programming, irrespective of which programming language you use.

What you will learn

  • Write reliable and scalable software based on the principles of functional programming
  • Explore advanced functional concepts such as lambdas, generic type parameters, and higher-order functions
  • Effectively solve complex architectural problems
  • Avoid unwanted outcomes such as errors or delays and focus on business logic
  • Write parallel programs in a functional style using the actor model
  • Use functional data structures and collections in your day-to-day work
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Length: 380 pages
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Table of Contents

16 Chapters
The Declarative Programming Style Chevron down icon Chevron up icon
Functions and Lambdas Chevron down icon Chevron up icon
Functional Data Structures Chevron down icon Chevron up icon
The Problem of Side Effects Chevron down icon Chevron up icon
Effect Types - Abstracting Away Side Effects Chevron down icon Chevron up icon
Effect Types in Practice Chevron down icon Chevron up icon
The Idea of the Type Classes Chevron down icon Chevron up icon
Basic Type Classes and Their Usage Chevron down icon Chevron up icon
Libraries for Pure Functional Programming Chevron down icon Chevron up icon
Patterns of Advanced Functional Programming Chevron down icon Chevron up icon
Introduction to the Actor Model Chevron down icon Chevron up icon
The Actor Model in Practice Chevron down icon Chevron up icon
Use Case - A Parallel Web Crawler Chevron down icon Chevron up icon
Introduction to Scala Chevron down icon Chevron up icon
Assessments Chevron down icon Chevron up icon
Other Books You May Enjoy Chevron down icon Chevron up icon

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Me ha gustado conocer algo más sobre esta manera de programación, la programación funcional aplicada en Scala. Volveré a vendedor, ya que sus servicios están a la altura de nuestros días. Gracias por todo.
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